Carrier dynamics in low-temperature grown GaAs studied by terahertz emission spectroscopy

Němec, H.; Pashkin, A.; Kužel, Petr; Khazan, M.; Schnüll, S.; Wilke, Ingrid

doi:10.1063/1.1380414

Cited by 94 publications

(60 citation statements)

References 28 publications

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“…Similar result (τ l~7 0 fs) has been obtained also after a quantitative comparison of the measured PL spectrum with the results of the numerical simulation by a combined Monte Carlo / molecular dynamics procedure [70]. Figure 11 shows a collection of electron lifetimes in the LTG GaAs grown at different temperatures and annealed at 600 o C [61,65,[70][71][72]. The available experimental data for the as-grown LTG GaAs [61,70] are also presented for comparison.…”

Section: Electron Trapping Timessupporting

confidence: 60%

Semiconductors for terahertz photonics applications

Krotkus¹

2010

J. Phys. D: Appl. Phys.

112

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Abstract:Generation and measurement of ultrashort, sub-picosecond pulses of electromagnetic radiation with their characteristic Fourier spectra that reach far into terahertz (THz) frequency range has recently become a versatile tool of the far-infrared spectroscopy and imaging. This technique -THz time-domain spectroscopy, in addition to a femtosecond pulse laser, requires semiconductor components manufactured from materials with a short photoexcited carrier lifetime, high carrier mobility, and large dark resistivity. Here we will review most important developments in the field of investigation of such materials. Main characteristics of low-temperature-grown or ion-implanted GaAs and semiconducting compounds sensitive in the wavelength ranges around 1 µm and 1.5 µm will be surveyed. The second part of the paper is devoted to the effect of surface emission of THz transients from semiconductors illuminated by femtosecond laser pulses. Main physical mechanisms leading to this emission as well as their manifestation in various crystals will be described.

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Section: Electron Trapping Timessupporting

confidence: 60%

Semiconductors for terahertz photonics applications

Krotkus¹

2010

J. Phys. D: Appl. Phys.

112

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“…This in turn is not identical to the photoelectron trap time, 1,[9][10][11] but is elongated by the intrinsic transit time of a space-charge dominated current pulse initiated by the shortliving photoelectrons between the electrodes. 9,12 The restriction on the capacitance first imposes upper limits on the device area and number of fingers.…”

mentioning

confidence: 99%

“…The 1.6 µm device most clearly shows that the photocurrent is governed by three regimes: 21 ͑1͒ an ohmic regime below 1 V / m; ͑2͒ a drift-velocity saturation at 1 -4 V / m; and ͑3͒ a quadratic behavior above E q0 =3 V/ m due to increase of e,trap , where E q0 is given by L · ͑1/ e +1/ h ͒ / ͑ h − e ͒. 14 Because e ӷ h and h ӷ e 14 one may estimate h · h Ϸ L / E q0 =5 ϫ 10 −9 cm 2 / V, while e · e Ϸ 1.5ϫ 10 −9 cm 2 /V ( e = 0.66 ps, e = 2250 cm 2 /Vs at T g = 250°C), 11,22 so that about 80% of the total observed dc photocurrent I dc is due to holes. This would explain the observed factor of 20 drop of generated power from near-dc ͑around 3 GHz͒ to 150 GHz, assuming h Ϸ 6 ps ͑Ref.…”

mentioning

confidence: 99%

“…The fitted response-time in P THz ͑ ͒ϳ1/͓1+͑2 · e · ͒ 2 ͔ is e = 0.8 ps at 12 V / m, while a zero voltage trap time for LT-GaAs grown at T g = 250°C and annealed at 600°C is expected at e,trap = 0.66 ps. 11 The bolometer was calibrated as follows: The difference of bolometer voltage response to two blackbodies at 300 and at 77 K was measured and in addition the normalized THz response spectrum of the bolometer was determined by using it as the detector in a commercial far-infrared Fouriertransform spectrometer. Then the blackbody power within the measured bandpass was calculated at the two temperatures, taking into account the known aperture and solid detection angle of the bolometer horn.…”

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confidence: 99%

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Large-area traveling-wave photonic mixers for increased continuous terahertz power

Michael

Vowinkel

Schieder

et al. 2005

Applied Physics Letters

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A large-aperture design for terahertz traveling-wave photomixers, continuously pumped free space by two detuned diode lasers, is proposed and experimentally verified for devices based on low-temperature-grown GaAs ͑LT-GaAs͒. It combines the advantages of conventional interdigitated small-area structures and traveling-wave devices. An output power of 1 µW at the mixing frequency of 1 THz was measured in initial testing, which meets local oscillator power requirements for superconducting heterodyne mixer devices. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1884262͔ Continuous-wave photonic mixer terahertz ͑THz͒ radiation sources are basically fast photoconductive switches modulated with the beat frequency of two detuned nearinfrared ͑IR͒ diode lasers. 1 One of the fastest materials to follow the beat frequency in the THz range is lowtemperature-grown GaAs ͑LT-GaAs͒ with photocarrier trap times down to 100 fs. 2 Besides the corresponding unmatched tuning range, photomixers are also particularly attractive for their all-solid state, noncryogenic, low power consumption, and relative low-cost approach. Therefore, they are interesting as local oscillators ͑LOs͒ for heterodyne submillimeter or terahertz receivers 3,4 based on superconductor-insulatorsuperconductor junctions ͑SIS͒ or hot-electron bolometers ͑HEB͒. Providing the power necessary for these mixers above 1 THz is a challenge, but is within reach of the current development of LT-GaAs photomixers. The latest report for smallest-area SIS junctions is p pump Ϸ 0.1 W at 1 THz at the mixer 5 ͑with a theoretical frequency dependency of p pump ϳ f 2 ͒, and for HEBs p pump Ϸ 0.2 W at 1.8 THz at the mixer Si lens 6 ͑with an expected frequency dependency of p pump ϳ f͒.With small-area photonic mixers, consisting of interdigitated metal-semiconductor-metal electrode structures, hereafter MSM ͓Fig 1͑c͔͒, it proved to be difficult to routinely reach these power levels above 1 THz. If small-area mixers are used with broadband antennas of load resistance, R a , the uncompensated device capacitance, C, introduces a rolloff, 2,7 ϳ1/͓1+͑2 · R a C · ͒ 2 ͔, which is usually around 1 THz. However, if it is located at the footpoint of resonant antennas, capacitance up to a certain value may be tuned out by the antenna inductance, 8 and the terahertz power at the resonance frequency, res , follows just the unavoidable rolloff, ϳ1/͓1+͑2 · e · res ͒ 2 ͔, given by the effective response time, e , for the electronic current seen locally at the electrodes. This in turn is not identical to the photoelectron trap time, 1,9-11 but is elongated by the intrinsic transit time of a space-charge dominated current pulse initiated by the shortliving photoelectrons between the electrodes. 9,12 The restriction on the capacitance first imposes upper limits on the device area and number of fingers. Because of a destruction intensity of Ͻ1.5 mW/ m 2 for LT-GaAs this limits IR pump power to Ͻ100 mW, so that improved passive thermal sinking is essential for small-area mixers, 3,13 unless coolin...

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“…While the dynamics of photocarriers in the surface-field, photo-Dember and photoconductive THz emitters has been well studied [19][20][21][22][23][24][25][26][27][28][29], very little attention has been paid to this aspect for photoconductive detectors. In this paper, we present a semi-classical Monte Carlo simulation of the current response of PCRs to pulsed THz radiation (section 2).…”

Section: Introductionmentioning

confidence: 99%

Simulation of fluence-dependent photocurrent in terahertz photoconductive receivers

Castro-Camus

Johnston

Lloyd‐Hughes

2012

Semicond. Sci. Technol.

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A semi-classical Monte Carlo simulation of carrier dynamics in photoconductive detectors of terahertz (THz) radiation is presented. We have used this simulation to elucidate the importance of carrier trapping in the operation of photoconductive detectors. Simulations of the detection of single-cycle THz pulses by photoconductive antennas based on GaAs with trap densities between 2 × 10 17 and 2 × 10 18 cm −3 are presented. We show that the high frequency (>1 THz) spectral response of photoconductive devices decreases with increasing excitation fluence. Our simulations reveal that this effect is a direct consequence of the saturation of trapping centres

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Carrier dynamics in low-temperature grown GaAs studied by terahertz emission spectroscopy

Cited by 94 publications

References 28 publications

Semiconductors for terahertz photonics applications

Semiconductors for terahertz photonics applications

Large-area traveling-wave photonic mixers for increased continuous terahertz power

Simulation of fluence-dependent photocurrent in terahertz photoconductive receivers

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